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Java&Xml教程（十）XML作为属性文件运用【XML教程】,Java，XML,属性文件

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我们一般会将Java运用的设置参数保存在属性文件中，Java运用的属性文件可所以一个一般的基于key-value对,以properties为扩展名的文件，也可所以XML文件.

在本案例中，將会向人人引见怎样经由过程Java顺序输出这两种花样的属性文件，并引见怎样从classpath中加载和运用这两种属性文件。
下面是案例顺序代码：
PropertyFilesUtil.java

package com.journaldev.util;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
import java.util.Set;
public class PropertyFilesUtil {

    public static void main(String[] args) throws IOException {
        String propertyFileName = "DB.properties";
        String xmlFileName = "DB.xml";
        writePropertyFile(propertyFileName, xmlFileName);
        readPropertyFile(propertyFileName, xmlFileName);
        readAllKeys(propertyFileName, xmlFileName);
        readPropertyFileFromClasspath(propertyFileName);
    }    /**
     * read property file from classpath
     * @param propertyFileName
     * @throws IOException
     */
    private static void readPropertyFileFromClasspath(String propertyFileName) throws IOException {
        Properties prop = new Properties();
        prop.load(PropertyFilesUtil.class.getClassLoader().getResourceAsStream(propertyFileName));
        System.out.println(propertyFileName +" loaded from Classpath::db.host = "+prop.getProperty("db.host"));
        System.out.println(propertyFileName +" loaded from Classpath::db.user = "+prop.getProperty("db.user"));
        System.out.println(propertyFileName +" loaded from Classpath::db.pwd = "+prop.getProperty("db.pwd"));
        System.out.println(propertyFileName +" loaded from Classpath::XYZ = "+prop.getProperty("XYZ"));

    }    /**
     * read all the keys from the given property files
     * @param propertyFileName
     * @param xmlFileName
     * @throws IOException 
     */
    private static void readAllKeys(String propertyFileName, String xmlFileName) throws IOException {
        System.out.println("Start of readAllKeys");
        Properties prop = new Properties();
        FileReader reader = new FileReader(propertyFileName);
        prop.load(reader);
        Set<Object> keys= prop.keySet();        for(Object obj : keys){
            System.out.println(propertyFileName + ":: Key="+obj.toString()+"::value="+prop.getProperty(obj.toString()));
        }        //loading xml file now, first clear existing properties
        prop.clear();
        InputStream is = new FileInputStream(xmlFileName);
        prop.loadFromXML(is);
        keys= prop.keySet();        for(Object obj : keys){
            System.out.println(xmlFileName + ":: Key="+obj.toString()+"::value="+prop.getProperty(obj.toString()));
        }        //Now free all the resources
        is.close();
        reader.close();
        System.out.println("End of readAllKeys");
    }    /**
     * This method reads property files from file system
     * @param propertyFileName
     * @param xmlFileName
     * @throws IOException 
     * @throws FileNotFoundException 
     */
    private static void readPropertyFile(String propertyFileName, String xmlFileName) throws FileNotFoundException, IOException {
        System.out.println("Start of readPropertyFile");
        Properties prop = new Properties();
        FileReader reader = new FileReader(propertyFileName);
        prop.load(reader);
        System.out.println(propertyFileName +"::db.host = "+prop.getProperty("db.host"));
        System.out.println(propertyFileName +"::db.user = "+prop.getProperty("db.user"));
        System.out.println(propertyFileName +"::db.pwd = "+prop.getProperty("db.pwd"));
        System.out.println(propertyFileName +"::XYZ = "+prop.getProperty("XYZ"));        
        //loading xml file now, first clear existing properties
        prop.clear();
        InputStream is = new FileInputStream(xmlFileName);
        prop.loadFromXML(is);
        System.out.println(xmlFileName +"::db.host = "+prop.getProperty("db.host"));
        System.out.println(xmlFileName +"::db.user = "+prop.getProperty("db.user"));
        System.out.println(xmlFileName +"::db.pwd = "+prop.getProperty("db.pwd"));
        System.out.println(xmlFileName +"::XYZ = "+prop.getProperty("XYZ"));        
        //Now free all the resources
        is.close();
        reader.close();
        System.out.println("End of readPropertyFile");
    }    /**
     * This method writes Property files into file system in property file
     * and xml format
     * @param fileName
     * @throws IOException
     */
    private static void writePropertyFile(String propertyFileName, String xmlFileName) throws IOException {
        System.out.println("Start of writePropertyFile");
        Properties prop = new Properties();
        prop.setProperty("db.host", "localhost");
        prop.setProperty("db.user", "user");
        prop.setProperty("db.pwd", "password");
        prop.store(new FileWriter(propertyFileName), "DB Config file");
        System.out.println(propertyFileName + " written successfully");
        prop.storeToXML(new FileOutputStream(xmlFileName), "DB Config XML file");
        System.out.println(xmlFileName + " written successfully");
        System.out.println("End of writePropertyFile");
    }

}

当运转这段代码时，writePropertyFile 要领会在生成上述两种花样的属性文件，并將文件存储在工程的根目录下。
writePropertyFile 要领生成的两种属性文件内容：
DB.properties

#DB Config file#Fri Nov 16 11:16:37 PST 2012db.user=user
db.host=localhost
db.pwd=password

DB.xml

<?xml version="1.0" encoding="UTF-8" standalone="no"?><!DOCTYPE properties SYSTEM 
"http://java.sun.com/dtd/properties.dtd"><properties><comment>DB Config XML file</comment>
<entry key="db.user">user</entry><entry key="db.host">localhost</entry><entry key="db.pwd">password</entry>
</properties>

须要注重的是comment元素，我们在运用prop.storeToXML(new FileOutputStream(xmlFileName), "DB Config XML file");这段代码时第二个参数传入的是解释内容，假如传入null，生成的xml属性文件將没有comment元素。
控制台输出内容以下：

Start of writePropertyFile
DB.properties written successfully
DB.xml written successfully
End of writePropertyFile
Start of readPropertyFileDB.properties::db.host = localhostDB.properties::db.user = 
userDB.properties::db.pwd = passwordDB.properties::XYZ = nullDB.xml::db.host = 
localhostDB.xml::db.user = userDB.xml::db.pwd = passwordDB.xml::XYZ = null
End of readPropertyFile
Start of readAllKeysDB.properties:: Key=db.user::value=userDB.properties:: 
Key=db.host::value=localhostDB.properties:: Key=db.pwd::value=passwordDB.xml:: Key=db.user::value=userDB.xml:: 
Key=db.host::value=localhostDB.xml:: Key=db.pwd::value=password
End of readAllKeys
Exception in thread "main" java.lang.NullPointerException
    at java.util.Properties$LineReader.readLine(Properties.java:434)
    at java.util.Properties.load0(Properties.java:353)
    at java.util.Properties.load(Properties.java:341)
    at com.journaldev.util.PropertyFilesUtil.readPropertyFileFromClasspath(PropertyFilesUtil.java:31)
    at com.journaldev.util.PropertyFilesUtil.main(PropertyFilesUtil.java:21)

这里报了空指针非常，原因是生成的文件保存在工程的根目录下面，而读取时是从classpath下读取，將上面生成的两个属性文件拷贝到src下再次运转顺序即可。

我们一般会将Java运用的设置参数保存在属性文件中，Java运用的属性文件可所以一个一般的基于key-value对,以properties为扩展名的文件，也可所以XML文件.
在本案例中，將会向人人引见怎样经由过程Java顺序输出这两种花样的属性文件，并引见怎样从classpath中加载和运用这两种属性文件。
下面是案例顺序代码：
PropertyFilesUtil.java

package com.journaldev.util;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
import java.util.Set;
public class PropertyFilesUtil {

    public static void main(String[] args) throws IOException {
        String propertyFileName = "DB.properties";
        String xmlFileName = "DB.xml";
        writePropertyFile(propertyFileName, xmlFileName);
        readPropertyFile(propertyFileName, xmlFileName);
        readAllKeys(propertyFileName, xmlFileName);
        readPropertyFileFromClasspath(propertyFileName);
    }    /**
     * read property file from classpath
     * @param propertyFileName
     * @throws IOException
     */
    private static void readPropertyFileFromClasspath(String propertyFileName) throws IOException {
        Properties prop = new Properties();
        prop.load(PropertyFilesUtil.class.getClassLoader().getResourceAsStream(propertyFileName));
        System.out.println(propertyFileName +" loaded from Classpath::db.host = "+prop.getProperty("db.host"));
        System.out.println(propertyFileName +" loaded from Classpath::db.user = "+prop.getProperty("db.user"));
        System.out.println(propertyFileName +" loaded from Classpath::db.pwd = "+prop.getProperty("db.pwd"));
        System.out.println(propertyFileName +" loaded from Classpath::XYZ = "+prop.getProperty("XYZ"));

    }    /**
     * read all the keys from the given property files
     * @param propertyFileName
     * @param xmlFileName
     * @throws IOException 
     */
    private static void readAllKeys(String propertyFileName, String xmlFileName) throws IOException {
        System.out.println("Start of readAllKeys");
        Properties prop = new Properties();
        FileReader reader = new FileReader(propertyFileName);
        prop.load(reader);
        Set<Object> keys= prop.keySet();        for(Object obj : keys){
            System.out.println(propertyFileName + ":: Key="+obj.toString()+"::value="+prop.getProperty(obj.toString()));
        }        //loading xml file now, first clear existing properties
        prop.clear();
        InputStream is = new FileInputStream(xmlFileName);
        prop.loadFromXML(is);
        keys= prop.keySet();        for(Object obj : keys){
            System.out.println(xmlFileName + ":: Key="+obj.toString()+"::value="+prop.getProperty(obj.toString()));
        }        //Now free all the resources
        is.close();
        reader.close();
        System.out.println("End of readAllKeys");
    }    /**
     * This method reads property files from file system
     * @param propertyFileName
     * @param xmlFileName
     * @throws IOException 
     * @throws FileNotFoundException 
     */
    private static void readPropertyFile(String propertyFileName, String xmlFileName) throws FileNotFoundException, IOException {
        System.out.println("Start of readPropertyFile");
        Properties prop = new Properties();
        FileReader reader = new FileReader(propertyFileName);
        prop.load(reader);
        System.out.println(propertyFileName +"::db.host = "+prop.getProperty("db.host"));
        System.out.println(propertyFileName +"::db.user = "+prop.getProperty("db.user"));
        System.out.println(propertyFileName +"::db.pwd = "+prop.getProperty("db.pwd"));
        System.out.println(propertyFileName +"::XYZ = "+prop.getProperty("XYZ"));        
        //loading xml file now, first clear existing properties
        prop.clear();
        InputStream is = new FileInputStream(xmlFileName);
        prop.loadFromXML(is);
        System.out.println(xmlFileName +"::db.host = "+prop.getProperty("db.host"));
        System.out.println(xmlFileName +"::db.user = "+prop.getProperty("db.user"));
        System.out.println(xmlFileName +"::db.pwd = "+prop.getProperty("db.pwd"));
        System.out.println(xmlFileName +"::XYZ = "+prop.getProperty("XYZ"));        
        //Now free all the resources
        is.close();
        reader.close();
        System.out.println("End of readPropertyFile");
    }    /**
     * This method writes Property files into file system in property file
     * and xml format
     * @param fileName
     * @throws IOException
     */
    private static void writePropertyFile(String propertyFileName, String xmlFileName) throws IOException {
        System.out.println("Start of writePropertyFile");
        Properties prop = new Properties();
        prop.setProperty("db.host", "localhost");
        prop.setProperty("db.user", "user");
        prop.setProperty("db.pwd", "password");
        prop.store(new FileWriter(propertyFileName), "DB Config file");
        System.out.println(propertyFileName + " written successfully");
        prop.storeToXML(new FileOutputStream(xmlFileName), "DB Config XML file");
        System.out.println(xmlFileName + " written successfully");
        System.out.println("End of writePropertyFile");
    }

}

当运转这段代码时，writePropertyFile 要领会在生成上述两种花样的属性文件，并將文件存储在工程的根目录下。
writePropertyFile 要领生成的两种属性文件内容：
DB.properties

#DB Config file#Fri Nov 16 11:16:37 PST 2012db.user=user
db.host=localhost
db.pwd=password

DB.xml

<?xml version="1.0" encoding="UTF-8" standalone="no"?><!DOCTYPE properties SYSTEM " 
<properties><comment>DB Config XML file</comment><entry key="db.user">user</entry><entry key="db.host">localhost</entry>
<entry key="db.pwd">password</entry></properties>

须要注重的是comment元素，我们在运用prop.storeToXML(new FileOutputStream(xmlFileName), "DB Config XML file");这段代码时第二个参数传入的是解释内容，假如传入null，生成的xml属性文件將没有comment元素。
控制台输出内容以下：

Start of writePropertyFile
DB.properties written successfully
DB.xml written successfully
End of writePropertyFile
Start of readPropertyFileDB.properties::db.host = localhostDB.properties::db.user = userDB.properties::db.pwd = passwordDB.properties::XYZ = 
nullDB.xml::db.host = localhostDB.xml::db.user = userDB.xml::db.pwd = passwordDB.xml::XYZ = null
End of readPropertyFile
Start of readAllKeysDB.properties:: Key=db.user::value=userDB.properties:: Key=db.host::value=localhostDB.properties:: Key=db.pwd::value=passwordDB.xml:: 
Key=db.user::value=userDB.xml:: Key=db.host::value=localhostDB.xml:: Key=db.pwd::value=password
End of readAllKeys
Exception in thread "main" java.lang.NullPointerException
    at java.util.Properties$LineReader.readLine(Properties.java:434)
    at java.util.Properties.load0(Properties.java:353)
    at java.util.Properties.load(Properties.java:341)
    at com.journaldev.util.PropertyFilesUtil.readPropertyFileFromClasspath(PropertyFilesUtil.java:31)
    at com.journaldev.util.PropertyFilesUtil.main(PropertyFilesUtil.java:21)

以上就是Java&Xml教程（十）XML作为属性文件运用的内容，更多相关内容请关注ki4网（www.ki4.cn）！

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